Mechanism of affecting the axial rotor stability and performance with center offset degrees of axial skewed slots

A subsonic axial rotor with axial skewed slot casing treatment (ASSCT) was investigated with experimental and numerical methods to explore the effects of the center offset degree (Cod) on the rotor stability and performance. Cod is defined as the ratio of the central difference between the rotor tip section and ASSCT to the rotor tip axial chord length. The Cod values are selected as 1.16, 0.608, 0, and −0.36, respectively. When the ASSCT is located upstream, the value of the Cod is positive. The experimental and unsteady calculated results show that the stall margin improvement (SMI) and peak efficiency loss (PEL) are reduced when the slots move to the rotor upstream or downstream. The slots with 0 Cod (ASSCT1) achieve 50% SMI with 8.67% PEL. The slots with 0.608 Cod (ASSCT2) gain 48.5% SMI with 2.12% PEL. The slots with 1.16 Cod (ASSCT3) and −0.36 Cod (ASSCT4) gain −3.41%, 20.1% SMI, respectively. Considering the compromise between the SMI and PEL for the rotor, ASSCT5 was designed by changing the slot number of ASSCT2 from 180 to 90. The unsteady calculated result shows that ASSCT5 can gain 22.28% SMI and 0.485% PEL. The detailed analysis of the flow field in the compressor tip passage indicates that there are adverse effects made by the slots on the flow field near the rotor blade tip leading edge for ASSCT3. Moreover, the ability of reducing the range of low-velocity zones for ASSCT4 is much lower than that for ASSCT1 or ASSCT2, and ASSCT1 generates bigger flow losses in the rotor tip passage than ASSCT2. The positive effects and flow losses made by the slots with 0.608 Cod both become smaller with the slot number decreasing from 180 to 90.